This information of angular position of the steering wheel can indeed be necessary for the fulfillment of various embedded functions, such as the automatic return of the steering to the midpoint, the controlling of the indicators of change in direction or the controlling of orientation of directional lamps, the intelligent parking assistance, etc.
As such, it is known, from the patent application FR-2 953 181, filed by the applicant, to use an algorithm which allows to define the multi-revolution instantaneous absolute position of the steering wheel.
According to this algorithm, the relative angular position of said steering wheel is first of all measured, by means of a sensor of the “resolver” type placed on the shaft of the assist motor coupled to the steering column, then is added to this relative measurement, to obtain the absolute position of the steering wheel, a corrective offset value which is calculated as the weighted average of the successively observed differences, gradually with the iterations, between on the one hand the value of the relative angular position measured in the considered iteration, and on the other hand an estimation of the absolute angular position of the steering wheel, obtained indirectly by applying laws involving dynamic running parameters, such as the speed difference between the rear wheels, reported by the anti-lock braking system ABS, or even the instantaneous yaw rate, provided by the trajectory control system ESP.
To these differences are assigned, for calculating the eventually retained offset, weighting coefficients that can be interpreted as a confidence index as to the accuracy of the estimation of the absolute angular position, according to the running conditions and the origin of the parameter used for the calculation.
Such an algorithm, called “angle finding” algorithm, presents undeniable advantages, particularly in that it allows to avoid the presence of an additional sensor that would be intended to directly measure the multi-revolution absolute angular position of the steering wheel, or even the need to make the vehicle run in a sustainable manner under particular conditions, and particularly in a straight line, to allow the initialization of the process of determining said absolute angular position.
However, the accuracy of said algorithm can sometimes, especially in extreme cases, deteriorate due to the fact that one or the other of the used dynamic models have reached their limits of validity.